Clear air turbulence (also referred to as “CAT”) is a leading cause of in-flight injuries and in severe cases can result in fatalities, resulting in significant losses in annual revenue to the aviation industry. Clear air turbulence is a turbulent movement of air masses in the absence of any visual clues (e.g., clouds). Clear air turbulence may be caused when bodies of air moving at widely different speeds meet and is frequently encountered by aircraft in the regions of jet streams. Clear air turbulence is usually impossible to detect with the naked eye and very difficult to detect with conventional radar, making it difficult for aircraft pilots to detect and avoid clear air turbulence.
Wake turbulence is another type of air turbulence that forms behind an aircraft as it passes through the air. Wake turbulence may include wake vortices that occur when a wing is generating lift. Air from below the wing is drawn around the wingtip into a region above the wing by the lower pressure above the wing, causing a wake vortex to trail from each wingtip. Wake turbulence is especially hazardous in the region behind an aircraft in the takeoff or landing phases of flight. To avoid wake vortices, the Federal Aviation Administration (FAA) has issued fixed aircraft separation standards for takeoff, approach, and landing. These aircraft separation standards result in delays that limit the volume of takeoffs and landings at airports, again resulting in significant losses in annual revenue to the aviation industry.
Existing systems for detecting wake and clear air turbulence are typically based on electromagnetic techniques, such as radar or LIDAR for example. However, such systems generally suffer a number of disadvantages including weight, power consumption, limited range, safety issues, and other considerations. For example, LIDAR based systems may detect wake and/or clear air turbulence from optically-generated digital representations of aerosols (e.g., water droplets) or aerial density fluctuations at flight altitudes. However, aerosols may not always be available in sufficient concentration and effective reflections from density fluctuations require significant amounts of power.